In a mobile communication system, when a call to a terminal has arrived, it is required to inform the terminal of the arrival of the call. A network of the mobile communication system manages the location information of the terminal using a location registration area, and a Location Area Identifier (LAI) is assigned to each location registration area. In the network, the message indicating the arrival of the call to the terminal is broadcasted to each of the terminals in the location registration area where the location of the terminal is registered. This process is called “paging” (see, for example, Non Patent Document 1).
A receiving process of paging information in a W-CDMA system is described with reference to FIG. 1.
First, a receiving apparatus receives a paging indicator channel (PICH) (step S2). The PICH includes a group ID of users who are to receive a paging channel (PCH). For example, as shown in FIG. 2, a flag for each group ID is provided. When, for example, the number of the user groups is 72, seventy two bits (flags) are provided. By using the PICH, more than one group ID may be called at a time.
Next, the receiving apparatus receives the PCH (step S4). The PCH is to be received by a user whose group ID is designated by the PICH. The PCH includes the user ID of a user who is being called. For example, the user ID is called “TMSI (Temporary Mobile Subscriber Identity)” and is expressed by 32 bits. In a W-CDMA system, a single PCH may call up to five user IDs. Further, a “Cause ID” indicating the reason of the call is added. The “Cause ID” may indicate communication types such as voice and has approximately 2 or 3 bits.
Next, the receiving apparatus receives a broadcast channel (BCH). The user who is called by the PCH checks current restrictions and receives the latest interference amount information before transmitting a random access channel (RACH) to perform an Initial Access (step S6).
Non Patent Document 1: “W-CDMA mobile communication system” by Keiji TACHIKAWA, Maruzen K. K. pp. 255-256.